The present invention relates to a device for straightening a metal strip having two strip drives which are suitable together to apply tension on the metal strip to straighten the metal strip, wherein at least one of the strip drives is a linear drive.
Devices for straightening metal strips are used in rolling and processing lines for metal strips. Metal strips are straightened for various purposes. For example, one case of application may be to improve the geometry and the flatness of the metal strips. Alternatively or additionally, the purpose of straightening may be to change certain mechanical properties of the metal strip with the deforming associated with the straightening, such as the yield strength or the break resistance.
Stretch-bend-straightening lines for straightening metal strips are known which have S-roller drives on the inlet side and the outlet side suitable to impose a tension to the strip, between which a bending stand is arranged with a plurality of bending rollers through which the metal strip passes. The stretch-bend-straightening to manufacture metal strips with defined flatness is then achieved from the interaction between strip tension and bending. The bending rollers are normally kept as small as possible in order to keep the strip tension imposed by the bending rollers as low as possible. This leads to residual stresses being introduced into the straightened metal strip which are subsequently released, worsening the geometry and the flatness of the strips once again. The pair of rollers for the S-roller drives which cause the build up and release of the strip tension also lead to a measurable worsening in the strip quality for each redirection. Therefore, for example, only strips straightened by stretching are used for heavily loaded components in aircraft construction, which however have to be manufactured in a discontinuous manner.
In the article “Neues Brems-und Zuggerust—ein Mechanik-Linearantrieb fur Walzwerke und Bandanlagen” by Leonhart Puppel, Klaus Bielefeld and the applicant, Norbert Umlauf, published in Verlag Stahleisen mbH, “Stahl und Eisen” 110 (1990), Number 2, pages 103 to 107, a mechanical linear drive is suggested which can be used instead of the S-roller drive in order to avoid the above mentioned disadvantage. The article also describes that for certain tasks it can be useful to assemble the linear drive in a compact manner and then only to straighten the metal strip under tension without a curving unit. A stand with an upper and a lower chain driven system with rubberised driver plates is described as a linear drive, which driver plates run in parallel over a certain distance. The metal strip is tensioned and transported between the driver plates running parallel. The drive is linear, by which, unlike with an S-roller drive, the metal strip is not bent.
Examples of linear drives suitable to linearly apply a driving force to a metal strip in a contact-based or in a contactless manner are further known from WO 00/27554 A1 and WO 2005/035158 A1.